The report describes how oil sands crude differs in chemical composition from other petroleum and the difficulty that this poses both in transportation and in cleanup when spills occur.

Tar sands diluted bitumen has 5-10 times as much sulfur as conventional crude and more chloride salts, the report said. Both substances can weaken pipelines and make them more likely to break during a pressure spike.

Refiners have reported finding more quartz sand and other solid material in tar sands diluted bitumen than other crudes, said the report, which also describes how at high pressure, this material “basically sandblasts” the inside of the pipe. Due to its thicker nature, increased heat and pressure are necessary to move bitumen through a pipeline.

"Our belief is that the report raises some important questions about transporting raw tar sands crude that should be clearly answered before we continue to allow it to flow through existing and proposed pipelines that are under a regulatory scheme that never considered these concerns," said Carl Weimer, executive director of the Pipeline Safety Trust and a co-producer of the report.

"We need answers to the valid safety concerns that diluted bitumen is more corrosive and contains more solids than traditional crude and may be more difficult to deal with if it spills," Weimer said.

The crude pipeline system in Alberta, which is newer but carries more tar sands oil than that in the US, has experienced 16 times more safety incidences due to internal corrosion than the US system, which the report describes as a strong indicator of the corrosive nature of raw tar sands oil.

The report’s authors looked at what they call the elevated risks in Enbridge’s Lakehead system in the Upper Great Lakes and TransCanada’s proposed Keystone XL line. The report highlighted 2010 Lakehead system failures that dumped nearly 1 million gal of oil into a creek and Michigan's Kalamazoo River. The report also examined the proximity of Keystone XL’s route in Nebraska to the Ogallala aquifer.

Oil sands producers exported 100,000 b/d of tar sands crude to the US in 2000 but plan to increase deliveries to as much as 1.5 million b/d by 2019, according to the report.